Embossing method for producing a structured voluminous nonwoven

ABSTRACT

The invention relates to a method for producing a structured voluminous non-woven fabric, comprising the following steps: producing a spunbonded non-woven fabric consisting of a plurality of monofilaments which are stretched only at 50 to 70% of the maximum possible stretch range to form a fiber skein and subsequent processing the raw non-woven fabric by means of a second pair of rollers ( 10   a, b ) with a metal outer jacket to improve the velvet finish. In the second pair of rollers, the positive elements of the positive roller are nops ( 11 ) arranged in rows and the surface of the negative roller has lamellas ( 13 ) which are arranged in an axial direction and provided with intermediate recesses ( 14 ) so that when the rollers roll against each other the lamellas engage in the channels left open by the nops.

BACKGROUND OF THE INVENTION

The invention relates to a method for producing a structured voluminousnonwoven comprising the following processing steps:

(a) manufacturing a spunbonded fabric consisting of a multitude ofmonofilaments that are stretched only at 50 to 70% of the maximumpossible stretch range and are deposited as a fiber strand,

(b) pressing and welding the fiber strand into a raw nonwoven by using afirst pair of rollers, and

(c) subsequently processing the raw nonwoven using a second pair ofrollers, where at least one of the outer roller surfaces is made ofmetal and that consists of a positive roller with numerous projectingelements distributed across the outer surface of the roller, and of anegative roller with equally numerous recesses, where during the rollingprocess the projecting elements engage in the recesses and post-stretchthe raw nonwoven in the area of the roller engagements.

The process described in the German Patent Application No. DE 195 47319.1 is based on the state-of-the-art according to U.S. patentapplication Ser. No. 5,399,174. This U.S. patent describes a laminatedfoil where a nonwoven layer, which consists of crimped polymeric fiberbundles and is laminated with a polymeric foil, is embossed with the useof rollers such that a connecting and decorating pattern is created andconnects the nonwoven with the foil. In the U.S. patent noted above, thesection “BACKGROUND OF THE INVENTION” also mentions that rollerembossing is a kind of method that alters the feel of the nonwoven andat the same time adds a decorative design. Reference is made to the U.S.Pat. No. 4,592,943, among others, according to which a prior method isused, where the nonwoven is heated while the nonwoven foil to beprocessed passes through two grids such that the grid in its specificdesign is transmitted to the nonwoven and a corresponding image isformed. Additional reference is made to the U.S. Pat. No. 4,774,124,which discloses a pattern roller embossing method.

Also known, from the U.S. Pat. No. 5,356,364, is an embossing method,where unmatched male (positive) and female (negative) elements of tworollers provide an embossing process that is said to provide aparticular fleeciness and embossing pattern.

SUMMARY OF THE INVENTION

Based on the teaching of the aforesaid German Patent Application 195 47319.1, the objective of the present invention is to provide a spunbondedfabric, which has already been deposited and already exhibits partiallybonded fibers and filaments corresponding to the nonwoven method, with adefined increase in volume, building upon the teaching of this patentapplication and improving it further.

Processing is carried out by using a second pair of rollers, where theouter surfaces of the rollers are made of metal, preferably both rollersof the same metal with a Rockwell Hardness (HRC) greater than 50, wherethe projecting elements of the positive roller are protrusions arrangedin rows and where the surface of the negative roller exhibits axiallyextending ribs or “lamellas” with recesses between them. With theseaxially arranged lamellas, which stretch across several protrusiondistances, improved stretching of the 70% pre-stretched material can beachieved, in particular, a special structure that opens at the tip ofthe protrusions which, in the industry, is referred to as “apperturizednonwoven”.

The openings are structured according to the geometry of the metalprotrusions. In accordance with the amount of protrusions, one obtains astronger opening and stronger perforation of the nonwoven. The openingshave a shape turned out towards the back side of the nonwoven. On theusage side, the openings appear like delicate funnels that can alsoreceive and transfer liquids. This effect is desired in a respectivecover-stock material because liquids can be taken up and passed on. Inaddition, the three-dimensional structure that the nonwoven has assumedprevents the liquid from returning to the surface. The surface remainsdry. In addition, the outside of the nonwoven has a soft, textile andpliable feel.

The fleeciness and the structure of the final product can largely bedetermined with the second pair of rollers. It is recommended to adjustthe distance of the rollers of the second pair of rollers, thusadjusting the engagement of the rollers into one another. Preferably,the rollers used have a protrusion height of between 0.8 and 2 mm andthe number of protrusions per 100 cm² roller surface is selected between2000 and 3000.

The temperature of the rollers is also important. For example, theprocess is carried out with the negative roller at a lower temperaturethan the positive roller. Examples of such temperatures for the positiveroller are between 175° C. and 190° C. and for the negative roller onlybetween 40° C. and 80° C.

To obtain a funnel-shaped structure of the nonwoven, it is recommendedthat the protrusions end in tips with the tips exhibiting, for example,the shape of onion towers, that is, they have a controlled shape that isfirst rounded and then ends in a tip. However, it is also possible tolet the tips end as pyramid-shaped tips with an acute angle of 90±20°.

Preferred initial materials for producing the nonwoven are polyethylene,polypropylene, polyesters or polyamide because these thermoplasticsexhibit the desired fleeciness in a particularly pronounced manner.

Conventional methods are suitable as manufacturing methods for thenonwoven; for example, fabrics used as nonwovens are those manufacturedby processes such as carding, airlaying or melt-blowing.

It is preferable to hold the raw nonwoven strand tight to the side atthe roller edges during the second stretching such that it does notshrink. During the second stretching, that is, during the first run ofthe raw nonwoven strand through the second roller pair, the fabric iskept at a temperature that basically corresponds to the temperature thatexisted during the first stretching. The roller temperature, therefore,is maintained somewhat above and below this temperature.

The invention further relates to a pair of rollers, where the outersurfaces of the rollers are made of metal, where the male elements ofthe positive rollers are protrusions arranged in rows and where thesurface of the negative roller exhibits lamella connectors in an axialdirection with recesses between said lamellas such that during therolling process the lamellas engage in the channels left open by theprotrusions and where the length of the lamella connectors surpasses atleast three protrusion distances.

For a full understanding of the present invention, reference should nowbe made to the following detailed description of the preferredembodiments of the invention as illustrated in the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic presentation of a device suitable for the process.

FIG. 2a shows in detail an embodiment of the stretching profile rollers.

FIG. 2b shows in an additional detail an embodiment of the stretchingprofile rollers according to FIG. 2a.

FIG. 3 is a magnified presentation of an overhead view in perspective ofa product manufactured according to the process.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will now be describedwith reference to FIGS. 1-3 of the drawings. Identical elements in thevarious figures are designated with the same reference numerals.

FIG. 1 shows schematically the manufacturing process of a structured,voluminous nonwoven. A storage silo 1 contains a thermoplasticgranulate, for example of polyethylene, polyester, polypropylene orpolyamide, that can be processed into the corresponding nonwoven. Itenters a heatable extruder and is advanced to the mouthpiece 3 of theextruder by the extruder screw 2′. Thereafter, the extruded material isfed into a spinning nozzle 5 via a guide trunk 4. From the spinningnozzle 5, the spun strand separated into very fine strings, enters astretching device 18 and then into the area of a chilling blower 22 usedto cool down the spun strand 6.

The individual fiber is not stretched entirely in the stretching device18. Advantageous is a stretching rate of 60 to 70% for polyethylene andpolypropylene, or of 50 to 70% for polyester or polyamide. This iscontrary to conventional stretching conditions where complete processstretching is preferred, for example, to save material.

The stretched spun strand 6 is placed on a grid conveyor 7 with a vacuumchamber 8 underneath, such that the spun strand lays flat on the gridconveyor 7. Said stand is then compressed between a first roller pair,namely calender rollers 9 a and 9 b. This processing step results in theraw nonwoven 12, which still has an area weight of about 20 g/m² and hasa thickness of only a few millimeters.

The raw nonwoven 12 produced in this manner only received a very loosefleece-hardening in the calender rollers 9 a and 9 b. only slightlocalized melting has been carried out in order to make materialprocessing easier.

The raw nonwoven 12 is now advanced to a second pair of rollers 10 a, 10b consisting of two stretching profile rollers. Roller 10 a is apositive roller with numerous protrusions 11 distributed across theouter surface of the roller, while the negative roller 10 b is providedwith equally numerous lamellas 13 with recesses 14 between saidlamellas. During the rolling process, the protrusions 11 engage in therecesses 14 and stretch the raw nonwoven in the areas of the engagement.

With this stretching process by the two rollers 10 a and 10 b, aprecisely defined localized over-extension of the fiber composite occursbecause the raw strand 12 is held tight at the border, that is, at theouter edges of the rollers 10 a and 10 b and cannot be pulled towardsthe center. This means, the nonwoven is held tight in one area and isextremely stretched in the area immediately adjacent. Depending on thedesign of the rollers, holding the fabric on the sides can also beignored.

As FIGS. 2a and 2 b show, the outer surface of the stretching profilerollers 10 a and 10 b is designed such that the portions sticking out,that is, the protrusions 11 protrude into the free spaces 14 between thelamellas 13 of the counter roller 10 b, while the flat zone of theembossing tool holds tight the portion of the stretchable nonwovenfabric. The roller and the counter roller are precisely matched. Theprotrusions 11 are shown as truncated pyramids. They can also be roundwith pointed ends. A configuration with the tip in an onion tower shapeis particularly well suited.

The lamellas 13 have a width of only about ⅓ to ⅕ of the free distancesbetween the protrusions 11. In the example of the embodiment, theystretch across the entire length of the roller. However, they may alsobe shorter or interrupted. However, the lamella length always bridges alarger number of protrusion distances, namely, at least three protrusiondistances.

The roller 10 a is provided with a sheath or coating of steel. Theprotrusions 11 are also made of steel. The sheath of roller 10 b is madeof steel as well. The steel used is one with a Rockwell Hardness of 62(cf. Meβmethoden [Measurement Methods] KLINGELNBERG, TechnischesHilfsbuch, Springer Verlag, 1967, 15. Auflage [Technical Aids, SpringerPublishing, 1967, 15^(th) Edition]).

The nonwoven 15 exiting from the rollers 10 a and 10 b has undergone asignificant change not only in its fiber length but also in thestructure of the nonwoven by the localized post-stretching. Through therespective roller design, the raw nonwoven receives a structure with athree-dimensional character, according to FIG. 3, as will be describedbelow.

In the stretching area, the individual fiber becomes extremely strongsuch that the volume character becomes durable as well. The feel of theentire nonwoven becomes significantly softer and more pliable andexhibits a changed water transport vector. The moisture is transportedfrom the surface to the back of the nonwoven along the protrudingendless fibers.

The distance of the rollers of the second pair of rollers, and thus theengagement of the rollers into each other is adjustable, as is known inroller technology. In the case at hand, the protrusion height is about1.5 mm with a distance of the protrusions from one another at about 1.5mm. The number of protrusions per 100 cm² is 2500. For example, a coverstock material is made of spunbonded fabric by depositing in the sameoperation polypropylene fibers with a density of 7 grams per cm² onto aconveyor belt and during the same run depositing melt-blownpolypropylene in an amount of 2×3 g per cm³ and by covering this with anadditional layer of 7 g per cm² polypropylene spunbonded fabric. Thiscomposite is initially fed to the roller device and spot-connected. Thepre-solidified spunbonded fabric on polypropylene base is then fed tothe second pair of rollers and perforated and reformed at a raisedpattern roller temperature of 175° C. and a lamella roller temperatureof 80° C.

According to FIG. 3, this results in a foil material that, percentimeter, exhibits about 5 funnel-shaped depressions 20 formed by themale embossing elements with a flat area 21 remaining between thedepressions. The height of the nonwoven, that is, the depth of the“cups” is about 1 mm. In the area of the male embossing elements, thematerial is perforated at the base and fully embossed, and can,therefore, be used as a hygiene product, for example as cover stock inthe manufacture of diapers or as cover layer in the manufacture offemale hygiene products.

The male embossing pattern that has resulted in the structuring ispyramid-shaped with a rectangular outline and an acute angle of 90°. Thedescribed method can also be used online with the spunbonded fabricproduction. However, a raw nonwoven can also be manufactured separatelyand then processed subsequently. A second nonwoven or a foil is to belaminated to the bulky nonwoven.

Similar to the main claim, in principle, the above mentioned method canbe used with all synthetic materials that are suitable for the melt-spinmethod with a pre-stretching step, such as polyethylene, polyester,polypropylene, polyamide and similar materials.

In principle, the above mentioned method is suitable for using andprocessing nonwovens of all conventional manufacturing methods,including nonwoven fabrics manufactured by processes such as carding,airlaying or melt-blowing.

Nonwoven fabrics manufactured from staple fibers according to thecarding method or the airlaying method that are manufactured from staplefibers, that is, fibers cut to a length of 3 to 6 cm of fibers of 2 to 5den by using a carding instrument, are slightly pre-embossed and thenentered into the reforming process subject to the invention.

With airlaid nonwoven fabrics, the staple fibers are transported throughthe air stream and deposited in a fine nonwoven form on a colander drum.This nonwoven pre-solidified by embossing is then entered into thereforming process subject to the invention.

Staple fiber nonwoven materials can be reformed because they still havea remaining capability for stretching stemming from the shiftability ofthe staple fibers and from their crimping. Carding and airlaid nonwovenfabrics are used in weight layers of 15 g/m² to 30 g/m², and if requiredwith even greater area weights.

Melt-blown nonwoven fabrics are obtained from a polymeric melt bytearing the drop exiting from the spinning nozzle into very fineindividual fibers. The individual fibers are taken up by the air streamand deposited in the form of a nonwoven onto a conveyer belt. Melt-blownfibers are very delicate and soft. Because of their insufficientstrength, they are often combined with other nonwovens. In hygieneapplications, melt-blown nonwovens made according to the invention canbe used by themselves or in connection with other nonwovens. Inparticular, a nonwoven fabric made of melt-blown fibers with an areaweight of 10 g/m² to 20 g/m² is well suited for reforming.

There has thus been shown and described a novel embossing method forproducing a structured voluminous nonwoven which fulfills all theobjects and advantages sought therefor. Many changes, modifications,variations and other uses and applications of the subject inventionwill, however, become apparent to those skilled in the art afterconsidering this specification and the accompanying drawings whichdisclose the preferred embodiments thereof. All such changes,modifications, variations and other uses and applications which do notdepart from the spirit and scope of the invention are deemed to becovered by the invention, which is to be limited only by the claimswhich follow.

What is claimed is:
 1. In a method for producing a structured voluminousnonwoven comprising the following processing steps: (a) manufacturing aspunbonded fabric consisting of a multitude of monofilaments that arestretched only at 50 to 70% of the maximum possible stretch range andare deposited as a fiber strand, (b) pressing and welding the fiberstrand into a raw nonwoven by using a first pair of rollers, and (c)subsequently processing the raw nonwoven by using a second pair ofrollers, where at least one of the outer roller surfaces is made ofmetal and that consists of a positive roller with numerous projectingelements distributed across the outer surface of the roller, and of anegative roller with equally numerous recesses, where during the rollingprocess the projecting elements engage in the recesses and post-stretchthe raw nonwoven in the area of the roller engagement, the improvementwherein the outer surfaces of the second pair of rollers are made ofmetal, wherein the projecting elements of the positive roller areprotrusions arranged in rows and wherein the surface of the negativeroller exhibits lamellas arranged in an axial direction with recessesbetween said lamellas such that during the rolling operation of therollers the lamellas engage in the channels left free by theprotrusions, which locally holds the nonwoven and stretches in the areaimmediately adjacent.
 2. Method as set forth in claim 1, wherein therollers of the roller pair consist of metal with basically the samehardness, namely a Rockwell Hardness (HRC) of greater than
 50. 3. Methodas set forth in claim 1, wherein the distance of the rollers of thesecond roller pair, and thus the mutual engagement of the rollers, canbe adjusted.
 4. Method as set forth in claim 1, wherein the height ofthe protrusions is between 0.8 and 2 mm.
 5. Method as set forth in claim1, wherein the distance of the protrusions from one another in linearorder is between 1 and 2.5 mm.
 6. Method as set forth in claim 1,wherein the number of protrusions per 100 cm² of roller surface isbetween 2000 and
 3000. 7. Method as set forth in claim 1, wherein thetemperature of the rollers of the second pair of rollers is setdifferently.
 8. Method as set forth in claim 7, wherein the temperatureof the negative roller is set to a temperature that is at least 20° C.lower than that of the positive roller.
 9. Method as set forth claim 1,wherein during the second stretching process the raw nonwoven strand iskept at a temperature that in general corresponds to the temperaturethat existed during the first stretching.
 10. Method as set forth inclaim 1, wherein the protrusions end in tips.
 11. Method as set forth inclaim 10, wherein the tips have an onion-tower shape.
 12. Method as setforth in claim 11, wherein the tips end as pyramid-shaped tips with anacute angle of 90±20°.
 13. Method as set forth in claim 1, whereinpolyethylene, polypropylene or polyamide is used as starting materialfor the production of the nonwoven.
 14. Method as set forth in claim 1,wherein fabrics used as nonwovens are those manufactured by processessuch as carding, airlaying or melt-blowing.
 15. Method as set forth inclaim 1, wherein during the second stretching the raw nonwoven strand isheld tight to the side at the edges of the rollers.
 16. Method as setforth in claim 1, wherein the second stretching that occurs in therecesses leads to a significant thinning even to a perforation of theraw nonwoven in the area of the roller engagement.
 17. Roller pair forcarrying out the method as set forth in claim 1, wherein the outersurfaces of the second pair of rollers are made of metal, the projectingelements of the positive roller are protrusions arranged in rows and thesurface of the negative roller exhibits lamellas arranged in an axialdirection with recesses between said lamellas such that during therolling operation of the rollers the lamellas engage in the channelsleft free by the protrusions.
 18. Roller pair as set forth in claim 17,wherein the rollers of the roller pair consist of metal with basicallythe same hardness, namely a Rockwell Hardness (HRC) of greater than 60.19. Roller pair as set forth in claim 17, wherein the distance of therollers of the second roller pair, and thus the mutual engagement of therollers, is adjustable.
 20. Roller pair as set forth in claim 17,wherein the height of the protrusions is between 0.8 and 2 mm. 21.Roller pair as set forth in claim 17, wherein the distance of theprotrusions from one another in linear order is between 1 and 2.5 mm.22. Roller pair as set forth in claim 17, wherein the number ofprotrusions per 100 cm² of roller surface is between 2000 and
 3000. 23.Roller pair as set forth in claim 17, wherein the protrusions end intips.
 24. Roller pair as set forth in claim 23, wherein the tips have anonion-tower shape.
 25. Roller pair as set forth in claim 24, wherein thetips end as pyramid-shaped tips with an acute angle of 90±20°.